The present invention relates to a plasma processing apparatus adjusted for a batch-processing of a plurality of wafers with plasma gases under individually different conditions, and more particularly to a plane parallel plate plasma processing apparatus adjusted for a batch-processing of a plurality of wafers with micro-wave plasma gases under a uniform condition or individually desirable conditions different from each other.
The plasma processing apparatus have widely been used for a plasma chemical vapor deposition and an etching process. In the plasma processing, process gas is excited at a high frequency to generate active plasma gas to be used for a surface processing of a wafer or a substrate. The typical conventional plasma processing apparatus was a single wafer type which is capable of processing a single wafer or substrate at a time. The wafers or substrates to be processed have various sizes. A substrate for a liquid crystal display panel tends to have a large size. In order to improve through put, it is required to install a plurality of the single wafer type plasma processing apparatus. This manner needs not only a high cost but also a large floor space.
In order to settle the above disadvantages, there has been developed a batch plasma processing apparatus which is capable of processing a plurality of wafers with plasma at a time. The batch plasma processing apparatus will be described with reference to FIGS. 1A and 1B. The batch plasma processing apparatus has a chamber 19 which accommodates a plurality of substrates 28 or wafers to be processed. The substrates or wafers are placed on a bottom electrode 21 provided on a sampling stage 23. Plasma gas in the chamber 19 is discharged via a discharge port provided between a bottom portion of the chamber 19 and the sampling stage 23. The bottom electrode 21 is electrically connected to a high frequency power supply 20 which is provided outside the chamber 19. The top portion of the chamber 19 is provided with a plurality of top electrodes 22 provided on a bottom of a ceramic plate. The top eIectrodes 22 are separated from each other by a plurality of microwave radiation ports 25 through which microwaves are radiated toward the substrates or wafers 28 on the bottom electrode. The outer side face of the top portion of the chamber 19 is provided with a microwave guide 27 for introducing the microwave into the chamber 19. The top portion of the chamber 19 is provided with a dielectric plate 24 made of Teflon for transmitting the microwave from the microwave guide 27 to the microwave radiation ports 25.
In the above plane parallel plate plasma processing apparatus, the microwave is introduced from the microwave guide through the dielectric plate member 24 and the microwave radiation ports 25 to be radiated toward the substrate or the wafers 28 so that the process gas is excited to generate a plasma gas having a high density. The generated plasma is accelerated by a high frequency electric field generated by a high frequency voltage applied to the bottom electrode 22 for processing the substrates or wafers 28 at a time.
The above plane parallel plate plasma processing apparatus adjusted for the batch processing of the plural wafers or substrates is, however, engaged with the following disadvantages. The microwave radiation ports vary in opening areas between the center and peripheral portions so that the microwave radiated is uniform in intensity. Notwithstanding, the plasma generated by the uniform microwave radiation varies in density. The variation in density of the generated plasma causes a variation in thickness of a CVD film deposited thereby or variations in depth and width of etching thereby.
The above plane parallel plate plasma processing apparatus adjusted for the batch processing of the plural wafers or substrates requires a large chamber like the chamber 19 illustrated in FIGS. 1A and 1B. When a pressure of the process gas in the chamber is reduced to not more than 0.1 Pa or in the vicinity of molecular flow range, then a variation in pressure of the process gas in the chamber 19 over positions is caused. At the position where the pressure is high, the plasma gas tends to include ions which radiates in an oblique direction to the surface of the substrates or the wafers 28. This makes it difficult to obtain a desired aspect ratio of the etching.
In the above circumstances, it has been required to develop a novel plane parallel plate plasma processing apparatus adjusted for a batch processing of a plurality of substrates and wafers under individually different conditions for process gas pressure and intensity of microwave radiation as well as high frequency voltage to thereby allow desirable plasma processing of a plurality of substrates and wafers at one time.